The present invention relates to a fuel injection device and a fuel injection method, in particular for a fuel reformer for generating hydrogen rich gas from hydrocarbon fuel, wherein the fuel, which is injected through the fuel injection device, is heated by a heating element arranged in the fuel injection device.
For the operation of fuel cells which provide electric energy for a vehicle, hydrogen is necessary. This hydrogen can be directly stored in a tank, but this storage is technically complicated and dangerous due to the explosiveness of hydrogen. Therefore, it has proven useful to generate a hydrogen rich gas from preferably liquid hydrocarbon fuel through catalytic conversion. The catalytic conversion of the hydrocarbons is carried out in several successive steps, the actual reforming, in which the hydrocarbons are broken down into the hydrogen rich gas comprising hydrogen, carbon monoxide, carbon dioxide and steam in accordance with the thermodynamic equilibrium, as well as a subsequent staged water-gas shift reaction, during which carbon monoxide and water are catalytically converted into carbon dioxide and hydrogen.
For the first step in this process, namely the catalytic conversion of hydrocarbon fuel to a hydrogen rich gas, a so called fuel reformer is used. For good operating modes of the fuel reformer it has been shown that a successful and efficient conversion of a hydrocarbon fuel into a hydrogen rich gas is, among others, dependent on a successful mixing of the reactants. For that mixing it has proven useful to spray the hydrocarbon fuel into the fuel reformer, whereby a good atomization or vaporization of the hydrocarbon fuel can be achieved.
The quality of the atomization or vaporization of the hydrocarbon fuel depends among other on the viscosity of the fuel. By preheating the hydrocarbon fuel, the viscosity of the fuel can be increased, whereby an advantageous level of viscosity of the hydrogen fuel can be achieved. For such an advantageous level of viscosity, the corresponding temperature of the hydrocarbon fuel is typically between circa 50° C. and circa 80° C.
From the state of the art, there are known a plurality of fuel injection nozzles with preheating elements for preheating the hydrocarbon fuel during a startup process and for keeping the fuel at the preferred temperature. Such fuel injection nozzles with heating devices are described for example in EP1323918, US 20060159437, EP1801907 or US20050227130.
The problem with these known fuel injection devices with preheating devices is how to regulate the temperature of the fuel after the startup process. Since known fuel reformers operate at temperatures between typically circa 600° C. and circa 900° C., the fuel injection nozzles, which are mounted at the fuel reformer are also heated. Thereby, also the temperature of the fuel increases which has the consequence that the desired temperature range of circa 50° C. to circa 80° C. for the fuel where advantageous levels of viscosity of the fuel can be achieved cannot be maintained.
Additionally, due to the high temperatures of the fuel injection nozzle coke and/or soot can deposit on the fuel injection nozzle. It is therefore necessary to control and regulate the temperature of the hydrocarbon fuel. For that purpose it is known to use complex temperature regulating circuits, which include e.g. a plurality of actuated valves to keep the hydrocarbon fuel in the preferred temperature range.
It is therefore desirable to provide a fuel injection device and a method for injecting hydrocarbon fuel into a fuel reformer which allows with a reduced number of control functions to maintain the temperature of the fuel within a wanted temperature range.
Aspects of the present invention are based on the idea to provide a fuel injection device, which is adapted to be mounted to a hot device, such as a fuel reformer or a gas turbine, and provides a cooling of the outside of the fuel injection device while simultaneously provides a heating of the hydrocarbon fuel by means of a heating device. By the simultaneous heating and cooling, hydrocarbon fuel having the desired viscosity for a good atomization is provided. The cooling of the outside of the fuel injection device has the further advantage that a heat transfer from the hot device, e.g. the fuel reformer, to the fuel injection device can be reduced, whereby the undesired heating of the hydrocarbon fuel due to the heat of the hot device prior to the injection can be prevented.
A fuel injection device according to an aspect of the invention may comprise a fuel injection device inlet for receiving hydrocarbon fuel, a fuel injection device socket, which is preferably adapted to be mounted to a fuel reformer, and a fuel injection device outlet for releasing hydrocarbon fuel, preferably into a fuel reformer. The heating device is preferably arranged near the fuel injection device inlet and can be thermally insulated from the cooling device.
According to a preferred embodiment, the cooling is arranged so that primarily the fuel injection device socket is cooled. This in turn results in a pre-cooling of the hydrocarbon fuel prior to its injection, as the fuel injection device socket is preferably in thermal contact with the hydrocarbon fuel. Since the fuel injection device socket is also in thermal contact with the fuel injection device outlet, the cooling of the fuel injection device socket also provides a cooling of the fuel injection device outlet. Thereby, also the deposit of coke at the fuel injection device can be minimized.
Further, by providing the cooling of the fuel injection device, the hydrocarbon fuel can be kept at a temperature below or at the temperature for the preferred fuel viscosity, even if the fuel injection device is subjected to a very hot environment, e.g. to the fuel reformer. It is further preferred to provide a temperature regulating element for sensing the temperature of the hydrocarbon fuel and/or regulating the heating device. Thereby, the hydrocarbon fuel can be heated, in case the temperature of the fuel is below a preferred temperature, and in case the hydrocarbon fuel is already at the preferred temperature, the heating of the fuel is not applied.
According to a preferred embodiment, a cooling device can be provided by supplying a cooling fluid, preferably cooling water, at the fuel injection device socket, and from there a cooling is also provided at the fuel injection device outlet, since the fuel injection device socket and the fuel injection device outlet are in thermal contact.
The cooling fluid is preferably supplied through a cooling fluid inlet pipe, which is preferably arranged in a space between an inner wall and an outer wall of the cooling device, and terminates near the fuel injection device socket, from where the cooling fluid may flow freely into the space defined between the inner wall and the outer wall of the cooling device. Preferably, the inner wall is, at least in this area, in thermal contact with the fuel injection device socket. Further a cooling fluid outlet pipe can be provided, which is adapted to collect and drain off the cooling fluid. Preferably, the cooling fluid outlet pipe is arranged near the fuel injection device inlet.
According to a further embodiment, an improved thermal contact between the fuel injection device socket and the cooling water is provided by arranging cooling fins at least partially around the fuel injection device socket, whereby the fuel injection device socket is cooled efficiently.
According to a further preferred embodiment, the hydrocarbon fuel is directed from the fuel injection device inlet through the fuel injection device socket to the fuel injection device outlet by a fuel directing element, such as a tube, around which the heating device can be arranged. Preferably, the heating device is an electrical heating wire which is wound around the fuel directing element. Advantageously, an electrical insulating layer can be arranged between the fuel directing element and the heating wire.
According to another advantageous embodiment, the heating wire is covered with a layer of thermal insulation. The thickness of the thermal insulation layer is preferably comparable to or greater than the thickness of the heating wire. Preferably, the insulation layer is covered by a cover element, which is preferably made from stainless steel, and can be designed as the inner wall of the cooling device.
The heat transfer to the fuel directing element and thereby the temperature of the fuel can be regulated by a simple thermostat which is preferably arranged near the heating element. The thermostat preferably senses the temperature of the fuel directing element and thereby of the fuel and controls the heating device in accordance to the sensed temperature.
According to a further preferred embodiment, the thermostat can regulate the heating wire, whereby the hydrocarbon fuel can be kept at the preferred temperature in the range of circa 50° C. to circa 80° C.
Since the thermal insulation layer keeps the heated fuel apart from the cooling device, a temperature control of the cooling device is not necessary. Therefore, according to a further preferred embodiment, the amount of cooling fluid needs not to be regulated.
According to a further preferred embodiment, an outer tube, preferably in the area of the fuel injection device socket, is arranged around the outer wall of the cooling device, wherein preferably the diameter of the outer tube is greater than the diameter of the outer wall of the cooling device. Therefore, the outer tube provides a thermal insulation of the outside of the fuel injection device to its environment, e.g. a fuel reformer wall. Preferably, the diameter of the outer tube is adapted to provide a maximal heat conducting distance while in parallel not unduly increasing the overall diameter of the fuel injection device. In the space between the outer wall of the cooling and the outer tube, a thermal insulating material can be advantageously provided. Since this outer tube keeps the (temperature regulated) fuel injection device away from a hot environment, e.g. the hot fuel reformer walls, the heat influence of the environment, e.g. of the fuel reformer, to the fuel injection device and thereby to the fuel is considerably reduced.
Further advantages and preferred embodiments are defined in the claims, the description and the Figures.